Teach erlang:is_builtin/3 that erlang:apply/3 is built-in

erlang:is_builtin(erlang, apply, 3) returns 'false'. That seems to be
an oversight in the implementation of erlang:is_builtin/3 rather than
a conscious design decision. Part of apply/3 is implemented in C (as a
special instruction), and part of it in Erlang (only used if apply/3
is used recursively). That makes apply/3 special compared to all other
BIFs.

From the viewpoint of the user, apply/3 is a built-in function,
since it cannot possibly be implemented in pure Erlang.

Noticed-by: Stavros Aronis

1 files changed, 9 insertions, 0 deletions

diff --git a/erts/emulator/beam/beam_emu.c b/erts/emulator/beam/beam_emu.c
index a42ce1c9f1..faf496a030 100644
--- a/erts/emulator/beam/beam_emu.c
+++ b/erts/emulator/beam/beam_emu.c
@@ -6752,6 +6752,15 @@ erts_is_builtin(Eterm Mod, Eterm Name, int arity)
     Export e;
     Export* ep;
 
+    if (Mod == am_erlang && Name == am_apply && arity == 3) {
+	/*
+	 * Special case. apply/3 is built-in (implemented in C),
+	 * but implemented in a different way than all other
+	 * BIFs.
+	 */
+	return 1;
+    }
+
     e.code[0] = Mod;
     e.code[1] = Name;
     e.code[2] = arity;